Conventionally, it was impossible to determine a relationship between a boiler performance index or a furnace heat absorption rate and each characteristic component of a mixed coal. Even determined, it was impossible to reflect the design structural characteristics of a boiler provided in a thermoelectric power plant on determination of a relationship between a boiler performance index or a furnace heat absorption rate and each characteristic component of mixed coal.
Therefore, conventionally, influence of a mixed coal can be predicted and evaluated only by creating a combustibility index obtained using a calculation equation based on physical properties of the mixed coal without considering and reflecting structural characteristics of a thermoelectric power plant.